The present invention relates generally to smart skin structures with vibration energy managing and steering capabilities and in particular the present invention relates to managing vibrations in the skin or shell of a system, subcomponent, device, or structure.
Current passive vibration suppression methods are grouped in three main areas: energy isolation, energy absorption, and energy dissipation through damping material and/or damping devices. As the name implies, absorbers are added single- or multiple-degree-of-freedom systems designed to absorb vibration energy, while isolators intercept the flow of vibration energy and prevent transmission to or from the system under consideration. Note that in the former, the energy is taken out of the primary system and directed to the absorbers while in the latter case, the energy is trapped to either side of the isolators. In the case of added damping, however, energy is dissipated in the form of noise and/or heat. There are many advantages for using these passive methods. Vibration isolators, absorbers, and added damping elements are well understood and have relatively simple mathematical models to aid in incorporating them in the design stage, and have been used by designers and engineers for over a century. They may be easy to manufacture and low cost to apply. However, passive methods have a few important performance disadvantages. Isolators and absorbers are usually tuned to one or a few selected resonant frequencies and, therefore, they are most effective within a narrow band around the selected resonant frequencies. Their performance degrades away from the designed frequency ranges. In certain cases, they may even amplify undesired vibrations.
Vibration isolators are not effective when severe shock or vibratory loads are present. The primary role of added damping in a structure is to take out more energy at a faster rate. Thus, their performance depends on how well and how much energy is delivered to the damping mechanism by the structure. Because structural vibrations are maximum at resonance, damping treatment methods are most effective at and near the resonant frequencies. Weight penalty is a concern when absorbers or added damping elements are used to reduce low frequency vibrations. Furthermore, most damping materials have a limited temperature range and perform better at higher frequencies. Therefore, a more effective vibration suppression scheme with a broader frequency range is needed.
In recent years, a variety of AVC (Active Vibration Cancellation) methods have been introduced to actively suppress vibrations. Most of these AVC techniques are based on vibration concepts that have been combined with advances in microelectronics, signal processing, material science, and control strategies to make a more adaptable and effective vibration suppression system. In the case of the currently practiced AVC systems with feedback controllers, vibrations are measured, fed back to the controller, and an appropriate actuating action is taken. In this case, the actuator applies a force or moment to counteract the existing vibrations. In the case of AVC systems with feed-forward controllers, the source is measured, fed forward to the controller, and then an appropriate actuating action is taken. In this case, actuators are used to inject an identical disturbance with an appropriate phase shift with respect to the measured signal at or near the source. Even though both AVC methods are conceptually different, they have at least two common features: they both inject energy into the system to cancel the existing undesired vibrations or noise, and they operate in a reactive mode (i.e., sense, process, and respond). Current AVC methods are not capable of altering the flow of vibrational energy within the structure.
U.S. Pat. No. 6,116,389, entitled xe2x80x9cApparatus and Method for Confinement and Damping of Vibration Energy,xe2x80x9d issued Sep. 12, 2000, and U.S. Pat. No. 6,032,552, entitled xe2x80x9cVibration Control by Confinement of Vibration Energy,xe2x80x9d issued Mar. 7, 2000, address vibration problems by noting that it may not be possible or practical to completely suppress vibration for all parts of a system. The patents, however, recognize that it may be practical to redirect or confine vibration to less critical or more easily controllable regions. In these patents, the confinement is implemented by passive or semi-active means which controlled the position and/or stiffness of structural or machinery components.
Metallic and composite skins, such as panels surrounding an automobile, walls and wallpapers used in construction, and boxes containing computers, are very important and integral parts of a system. In particular, spaceships, aircraft, ships, and submarines have load-bearing skins that not only have to withstand severe aerodynamic and hydrodynamic loads (thus, load-bearing), but also must carry arrays of optical, acoustic, and radar-type sensors. One of the primary tasks of a skin is to protect its cargo and sensor arrays.
Currently all skins (i.e., aircraft skin, automobiles, appliances, etc.) are simply a relatively thin layer of either isotropic metal or multi layer composites. In addition to conventional tasks, it would be desirable to have a skin that has the ability to manage and steer vibration energy to minimize the damaging effect of vibratory loads. A skin that can control noise and vibrations, via the control of power flow and energy management, could be well suited to monitor the health of its host system (or component). That is, the skin could detect damages and cracks at early stage, and localize damage so it can be rapidly inspected and repaired before propagating to the rest of the system.
For the reasons stated above, and for other reasons stated below which will become apparent to those skilled in the art upon reading and understanding the present specification, there is a need in the art for intelligent skin that can be implemented to actively alter vibration energy within the structure.
The above-mentioned problems with structural vibrations and other problems are addressed by the present invention and will be understood by reading and studying the following specification.
The present invention provides a system that senses the amount, location, and type of disturbing energy and confines, diverts, and steers excess disturbing energy in order to protect itself and all components it carries from potential damage due to random propagation of excess disturbing energy.
In one embodiment, a skin structure comprises a skin, sensors coupled to the skin to measure vibrations of the skin, and actuators integral with the skin. The actuators can be selectively activated to apply forces to the skin to confine or redirect vibration energy to one or more predetermined skin regions. A passive element can then be used to dissipate the confined vibration energy. The forces to be applied can be determined by spatial derivatives of the vibrating system or through phase and magnitude of the detected vibrations. Using the magnitude and phase of the detected disturbance, the appropriate phase and magnitude of the forces applied by the actuators are determined.
In another embodiment, a structure having a skin material comprises an outer layer, sensors coupled to the outer layer to measure vibrations in the outer layer, actuators integral with the skin, and a controller coupled to the sensors to provide control signals to the actuators.
In another embodiment, a method is provided for controlling vibrations in a skin structure. The method includes detecting vibrations in the skin structure, and applying feedback forces to actuators integrally formed in the skin to confine or redirect vibration energy by creating an energy power flow pattern in the skin.
Another method of controlling vibrations in a skin structure is provided. The method comprises detecting vibrations in the skin structure, and processing the detected vibrations to determine appropriate feedback forces need to confine the vibrations. The feedback forces are compared to historical data and baseline data to determine if a defect is present in the skin structure. Finally, the feedback forces are applied by the actuators integrally formed in the skin to confine or redirect vibration energy.